Where my earlier population-consumption projections indicated that to avoid a world population collapse we could get by with a one percent annual increase in the fraction of renewable resources consumed to total consumption (by weight, per year) while keeping total consumption constant, my latest projections show that the rate must now be about three percent. Constant consumption buys us eight years over business as usual (which shows population dropping after 2021), with each quarter-percent increase in the renewable-to-total consumption rate adding about a year until we reach about two percent. The gain in years increases rapidly after that, reaching a maximum of 300 years at a rate of three percent. Keep in mind that these “rates” must be applied until we are practically only consuming renewables (resources that can be reused in a year). The final state of this trajectory (also called “steady state”) is a condition of constant consumption and population, maintained entirely by a renewable resource base.
One problem with this solution is that my calculations show that even if we used all of the renewable resources the biosphere could provide, we would be unable to satisfy more than about one-third of our consumption this way. We will need to find some other source by about the same time we would start losing population if we kept growing our consumption. If our energy needs were met directly from the Sun or some other non-biological source, we might come close.
I estimate that at the three percent rate, we have less than 35 years to reach total renewably supplied consumption (passing 60 percent in 2030). The fastest and least costly approach would be to rely entirely on Nature as soon as possible, since technological fixes would almost by definition involve the consumption of more non-renewable resources. A better use of our technology might be the controlled shutdown and mitigation of the most harmful products of our civilization, such as nuclear material, plastics, and other chemical compounds that might be harmful to life. We probably don’t have enough time or resources left to serve what is perhaps our most important function: spreading life to other planets, and protecting life here from asteroid and comet impacts. Settlement of space might still be an option if a case could be made that new resources would be made available -- and safely -- before we run out here; such an option, in my view, is the only hope we have of continuing something like our present civilization.